In a large bowl, mix together 1⅓ cup of the flour, ½ teaspoon salt, baking powder, and the turmeric.
Add the beer and mix with a wooden spoon or a spatula. The batter should be the consistency of a pancake batter. Cover and chill in the refrigerator for 60 minutes.
When the batter is ready, heat the oil in a deep fryer to 300-320°F. The oil is hot enough when you add a bit of the batter and it starts bubbling immediately.
Cut the fish into even pieces, if not already, and pat dry with a paper towel and sprinkle both sides generously with salt and pepper.
Add the remaining flour to a shallow bowl and prepare the fish by flouring each piece on all sides and dipping it into the batter.
Then carefully add each piece into the oil and fry for 4 to 5 minutes or until golden brown on all sides. Hold the fish in the middle, dip it in and hold it for a couple of seconds until it starts swimming. Then let go. This helps to prevent the fish from sinking down and the batter sticking to the bottom.
Place cooked pieces of fish on folded paper towels. Serve hot with vinegar, lemon juice, and tartar sauce.